THE PREPARATION OF ANIMAL TISSUES. 41 



number to correspond with the note book attached 

 to each parcel. In this way many specimens can 

 be hardened together in the same fluid, and much 

 space and waste of fluid avoided without any risk 

 of confusion or error. No hard-and-fast line can 

 be drawn in respect of the time during which the 

 various organs and tissues should remain in the 

 hardening fluids; careful experiments and notes, 

 judgment and experience are necessary in this as 

 in all other chemical work. Again, many tissues 

 require hardening by different processes according 

 to the elements in their structure which it is desired 

 to demonstrate. For instance, to display the cor- 

 puscles and nerves of the cornea it must be treated 

 with gold, whilst in order to show the cell spaces 

 the silver process must be resorted to. The special 

 methods of hardening many of the various tissues 

 and organs will therefore be found included under 

 more than one process. 



Alcohol. 



When alcohol is employed as the sole hardening 

 agent it should be used strong (i.e., of 95 per cent.), 

 indeed it will be found necessary in some cases to 

 use absolute alcohol. The specimens are to be 

 immersed in an abundance of the spirit, which must 

 be frequently changed during the first few days. 

 It is advisable in many instances to suspend the 

 specimens, either wrapped in linen or by a strong 

 thread, in the alcohol. Some tissues will become 

 sufficiently hardened in a few days, whilst others, 

 and especially large specimens and whole organs, 

 will require weeks. The more frequently the 



